An armed police officer on patrol at Heathrow Airport's Terminal 5, as airport security was being increased at British airports after the United States called for heightened precautions amid reports two terror networks are working together on a bomb that could evade existing measures.

Britain Gives Police Power to Strip Suspected Terrorists of Passports

British Prime Minister David Cameron announced Monday temporary enhanced powers for police designed to keep Islamist extremists in Britain from traveling to Syria and Iraq. Cameron told parliament that police would have the ability to seize the passports of suspected militants en route to Syria or Iraq. The announcement came days after Britain raised its terror threat level from "substantial" to "severe," and follows the death of American journalist James Foley at the hands of an ISIS fighter who appeared to have a British accent. Cameron said British intelligence believes 500 people have traveled from Britain to fight with extremists groups in Syria and Iraq.

Cameron said authorities also needed stronger powers "to manage the risk by expected extremists already in the United Kingdom," and those who may travel into the UK from other countries. "Dealing with this terrorist threat is not just about new powers, it is about how we combat extremism in all its forms,” Cameron said. Outside of the country, Cameron said Britain and other world powers need to help Syria and Iraq form "free and open societies" because "we know that terrorist organizations thrive where there is political instability."